The most prevalent form of urinary dysfunction is incontinence. Urinary Incontinence is a clinical condition characterized by failure to hold urine in the bladder under normal conditions of pressure and filling. The most common forms of the disorder can arise from either a failure of muscles around the bladder neck and urethra to maintain closure of the urinary outlet (so-called stress incontinence) or from abnormally heightened commands from the spinal cord to the bladder that produce unanticipated bladder contractions (so-called urge incontinence). Many patients exhibit a grouping of symptoms suggesting that these disorders may occur simultaneously in the same individual (so-called mixed incontinence).
It is well known in the art that electrical stimulation in the region of the pelvic floor can decrease the severity of urinary incontinence. The improvement is believed to be attained through at least three mechanisms: (1) by changing the reflex thresholds of the bladder muscles responsible for bladder emptying, (2) by strengthening the muscles that maintain closure on the bladder outlet, and (3) by changing the state of the neural pathways, musculature and/or bladder during and beyond the period of stimulus application.
The therapies currently available for urinary incontinence have generally been directed at improving muscle condition, as disclosed, e.g., in applicant's prior document WO97/18857 (PCT/US96/18680), published 29 May 1997. Bladder hyperreflexia and detrusor instability have proven more difficult to treat. However, evidence in the art suggests that many individuals with these conditions can be improved by stimulating peripheral nerves or nerve roots continuously or intermittently to modulate transmission of excitatory nerve signals to the bladder muscles.
Several external and implantable approaches have been used to stimulate the nerves supplying the bladder and pelvic region in order to decrease the episodic incidences of unintentional bladder emptying. Those that strengthen periurethral muscles have usually employed vaginal or anal electrode assemblages to stimulate muscle contractions repeatedly. These methods are limited in their portability and are often poorly accepted by patients because they are inconvenient and often associated with unpleasant skin sensations. Further, the methods are inadequate for the treatment of urge incontinence in which continual electrical stimulation is commonly needed to diminish or inhibit the heightened reflexes of bladder muscles.
The sacral nerve roots exert significant neural control over the process of urination. Neurostimulation of sacral nerve roots, in particular the S3 sacral nerve roots, has been applied therapeutically in patients with urinary incontinence. Sacral nerve root stimulation has also been applied to promote urination in patients who are unable to initiate voiding through normal neural mechanisms.
For the treatment of urge incontinence, surgically implanted stimulators under battery or radio-frequency control have been described in the art. These stimulators have different forms, but are usually comprised of an implantable control module to which is connected a series of leads that must be routed to nerve bundles in either the sacral roots emanating from the spinal cord, or the nerves supplying muscles, skin or other structures in the pelvic region. The implantable devices are relatively large and expensive. In addition, they require significant surgical procedures for placement of electrodes, leads, and processing units. These devices may also require an external apparatus that needs to be strapped or otherwise affixed to the skin. Thus, their use has generally been confined to patients with severe symptoms and the capacity to finance the surgery.
These same types of therapies have been used to treat fecal incontinence and other bowel dysfunctions, with the same drawbacks. For instance, neurostimulation of sacral nerve roots has been investigated for therapeutic application in patients with fecal incontinence. Sacral nerve root stimulation has also been applied to promote defecation in patients who are unable to initiate voiding through normal neural mechanisms. As with known treatments for urinary dysfunction, currently available devices have several drawbacks, such as size (of internal and/or external components), discomfort, inconvenience, complex surgical procedures, and/or only acute or intermittent use. Other devices used for both urinary and bowel dysfunctions require that a needle electrode(s) be inserted through the skin during stimulation sessions. These devices may only be used acutely, and may cause significant discomfort.
Recently, small, implantable microstimulators have been introduced that can be injected into soft tissues through a cannula or needle. What is needed is a way to effectively use such small, fully implantable, chronic neurostimulators for the purpose of treating urinary and/or bowel dysfunction.